There are numerous processing methods for manufacturing rotationally symmetric precision parts, such as gear wheels. Typically, the precision part is measured during or after the processing.
In order to be able to check the precision of the processing of a precision part after processing, the precision part may be removed from the processing machine and clamped in a special measuring system, for example, where it is scanned and measured using sensors. Numerically controlled measuring devices are preferably used for this purpose. Typically, a rotationally symmetric precision part is clamped between a lower centering point and upper centering point for measuring. The lower centering point is seated on a table which may be moved precisely into different angular positions by a drive. The precision part is pressed against the lower centering point because of its intrinsic weight and the contact pressure which originates from the upper centering point. A rotational motion of the lower centering point is thus transmitted one-to-one to the precision part. The upper centering point only revolves, it is not also driven.
The present patent application is particularly concerned with CNC-controlled gear tooth measuring centers which are suitable for checking spur gear teeth, as well as pinion and shaving cutters, worms and worm gears, hobbing cutters, bevel gears, and general dimensional, shape, and position deviations on rotationally symmetric workpieces, for curve and camshaft measurement, or even for rotor measurement.
Investigations have shown that in precision parts having a small mass and a small diameter, such a construction having a lower centering point and an upper centering point is sufficient in order to rotate the precision part in solidarity with the lower centering point. Such a construction is sufficient above all if one operates using small angular accelerations.
Special measuring systems are increasingly used in order to measure precision parts having a larger diameter and higher weight. In addition, it is a very important requirement in measurements of this type that they are performed very precisely but as rapidly as possible.
The typical measuring systems are not able to meet such requirements. Rapid measurement of a complete precision part makes it necessary for multiple angular positions to be approached within a very short time and for a measurement sensor to scan the precision part in each angular position. The measuring systems are designed so that measurements may be performed even during the rotational motion. During rotation of the precision part, high angular accelerations arise which have been shown to lead to slip between the lower centering point and the precision part. The angular position of the lower centering point, respectively the drive, and the precision part thus no longer correspond to one another.
In order to be able to handle the problem of slip, larger and heavier precision parts are clamped using a dog, which preferably allows a form fit. A “form fit” is understood to mean that the force transmission between the dog and the precision part occurs through their shape. The slip may thus be eliminated as much as possible. However, it is a disadvantage of this achievement of the object that the mounting is complex and time-consuming and form-fitting dogs of this type are costly and often also heavy. In addition, handling the form-fitting dogs is complex and there are precision parts on which such dogs may not be used, since they have no appropriate collar on the shaft, for example. It is a further disadvantage that in spite of the use of form-fitting dogs, situations may occur in which slip occurs. This may be the case, for example, if the dog was mounted incorrectly or too loosely.
It is an object of the present invention to provide a device and a corresponding method which allows even larger or heavier precision parts to be measured rapidly and reliably.